1. Field
The present invention relates to an access control apparatus and an access control method of controlling I/O access to file(s) in a multi-processor system.
2. Description of the Related Art
Recently, a multiprocessor system has been developed in which multiple CPUs (Central Processing Units) execute multiple tasks in parallel, as a technique for executing various tasks in a data processing system In this multi-processor system, resource conflicts among tasks frequently occur. However, since an I/O (Input/Output) access operation related to a file and the like in a general-purpose server and the like is a very low-speed operation, relative to programs operating in an internal memory of a data processing system, a large amount of time is spent for processing of tasks waiting to be processed once waiting for I/O processing occurs. Especially, if a high-priority task is delayed because of waiting for I/O processing, data processing of the multi-processor system is seriously influenced, and a large amount of delay in data processing is caused.
In a typical I/O (file) access control, FIFO (First In First Out) queue control is performed, and I/O access is permitted in an order in which requests for I/O access have been made. Therefore, there is a problem that an I/O request from a high-priority task is made to wait (is not given priority) because of an I/O request from a low-priority task.
Japanese Patent Laid-Open No. 2005-301854 discusses an information processing apparatus as described below. The information processing apparatus processes an I/O request from an application against a recording medium so as to control I/O accesses according to priorities of tasks. The information processing apparatus sets a specific priority for an I/O request from an application to store the I/O request into a queue, and processes the I/O request stored in the queue according to the priority.
Japanese Patent Laid-Open No. 8-241214 discusses a data processing system. When multiple tasks request to read the same file, the data processing system divides the file into blocks and changes the number of blocks to be read by each task according to the priority. Thereby, the data processing system processes the multiple tasks in parallel.
Japanese Patent Laid-Open No. 7-73143 discusses an input/output priority order control method. Using the input/output priority order control method, it is possible to automatically determine and change the input/output priority of each transaction on the basis of the number of processings of the transaction for each time period Then, using the input/output priority order control method, it is possible to perform access to a file apparatus on the basis of the changed input/output priorities.